Process of producing porous paper



ratentecl May 6, 1930 UNITED STATES ATENT orrica GEORGE IJ- SCHWARTZ,OIE WILMINGTON, DELAWARE, ASSIGNOR .TO I/DU PONT DE NEMOURS & COMPANY,OF WILMINGTON, DELAWARE, A CORPORATION OF DELA- WARE PROCESS OFPRODUCING POROUS PAPER No Drawing.

This invention relates to a process of producing a cellulose fibre matsuitable on account of its high degree of porosity and other desirableproperties for paper towels or other absorption purposes. v

There is disclosed in U. S. Patent, Serial No. 1,038,086, to A. L.Clapp, the treatment of paper with caustic of mercerizing strength(usually around 18%) and at a normal tem- 19 perature.

In my copending application, Serial No. 232,192, filed November 11,1927, I have disclosed a process of gelatinizing cellulose fibres bytreating them in the form ofa paper mat with caustic soda at a lowtemperature and in a definite concentration range. In this treatment thefibres become gelatinized and swell, and, after removing the reagent,the fibres return approximately tot-heir normal volume.

20 As a result, the paper is puffed and becomes highly porous. g

An object of my present invention is a process of making absorbent paperfrom cotton fibres. A further ob ect of my present 1nven- 153515 aprocess of making absorbent paper from such fibres as linters and hullfibres that have been given a certain preliminary treatment such ascooking in dilute caustic sod a.

sti ur ier o ec o my inven 1011 1s the process of making absorbent paperfrom paper containing-a mixture of reactive fibres, such, for example,as cooked cotton linters, with non-reactive or slightly reactive fibres,such, for example, as uncooked cotton linters,

' kraft, jute, etc. Other objects will appear as the descriptionproceeds.

I have now found that a good quality of porous absorbent paper may beobtained by treating the paper made from certain grades of fibres withunder conditions out side of the range disclosed in my copendingapplication aforesaid. According to my present invention paper made fromcotton fibre may be treated with practically any concentration ofcanstie-fmnnmjtnantemperat ire from around 0 up to 104, and a, pr'od-11mm porous and absorbent for most commercial purposes. Under theseconditions, the fibres are not gelatinized but become permanently curledApplication filed June 6, 1928. Serial No. 283,446.

so that the mat decreases in density to a marked extent.

Particular features of my invention reside in the use of papercontaining cooked cotton fibres, or cooked cotton fibres mixed withother less reactive fibres, and treatin the fibres above thegelatinizino temperature. I have found that when a mixture of cookedbleached linters and uncooked linters, kraft,

\ -or jute are used, thenon-reactive or less r-e- 'iJ/ClllVG fibres holdthe mass together and the reactive fibres furnish the intense puffingwhich is so desirable.

- The following steps are given as specific embodiments of my improvedprocess, but it is to be understood that these are illustrative only andare not to be taken as limitations of my invention.

I. Short cotton fibres, for example, linters or hull fibres, are treatedwith or without pr V v at about 1-10% concent I. A paper mat is madeeither from the cooked cotton fibres alone, or from these fibres mixedwith another grade of fibres,

preferably wood or hemp, which are less reactive with caustic soda underthe conditions of treatment in step III, following.

III. This paper mat is treated with caustic soda of mercerizingstrength, whgzh is ordinaril abo allglifillefiwd litloove a mlnlmum ofabout 8%. The strength as stated applies to the solution in actualcontact with the fibres. The temperature of this treatment is preferablylow', especially where high porosity of product is desired, but thetemperature should be kept above the point at which the fibres aregelatinized to a noticeable degree by caustic of the concentration used.The minimum temperature of the caustic treatment, therefore, is notfixed, but varies with the fibres used and with the concentration of thecaustic. This is a point which is readily determined for any given fibreand reagent. At higher temperatures, that is, at temperatures from to104 0., the curling effect on the fibres and the pul'fing efiect on thepaper are less marked than at lower temperatures. In the present case,it therefore follows that for given fibres and concentration of caustic,the lower operative temperature limit is the upper temperature limit atwhich the fibres are gelatinized, and the upper operative temperaturelimit is the lower temperature limit at which the fibres undergodegradation in the presence of oxygen. Depending on the grade of fibresand the concentration of the caustic, this degradation effect becomesnoticeable in the presence of a small proportion of oxygen attemperatures around 100 C.

IV. The paper is washed to free it from the reagent.

As many apparently widely different embodiments of this invention may bemadewithout departing from the spirit and scope thereof, it is to beunderstood that I do not limit myself to the specific embodimentsthereof except as defined in the appended claims.

I claim:

1. A process for producing a porous felted cellulose fibre product whichcomprises treating a cellulose fibre mat made from cooked cotton withaqueous caustic solution, at a temperature a hoye the elatinizing pointof the fibres and less than 104 C.

2. A process for producing a porous felted cellulose fibre product whichcomprises treating a cellulose fibre mat made from cooked cotton fibresmixed with a grade of fibre less reactive with caustic under theconditions of mercerizing, and treating the fibres at a temperature justabove the gela-tinizing point of the reactive fibres and less than 104C.

3. A process of making a porous felted cellulose fibre product whichcomprises forming a paper mat from cooked cotton fibres, treating thepaper mat with caustic of mercerizing strength at a temperature justabove the gelatinizing point, and washing the paper free from the agent.

4. A process of making a porous felted cellulose fibre product whichcomprises treating a paper mat made from cooked cotton fibres, withcaustic of a strength of approximately 8% to 18%, and at a temperatureabove 0 C. but less than 104 C., and washing the paper free from thecaustic.

5. A process of making a porous felted cellulose fibre product whichcomprises treating a paper mat made from cooked cotton fibres, withcaustic of a strength of approximately 8% to 18%, and at a temperatureabove 0 C. but less than (3., and

washing the paper free from the caustic.

In testimony whereof, I afiix my signature.

GEORGE L. SCHWARTZ.

CERTIFICATE OF CORRECTION.

Patent No. 1,757,757. -Granted May 6, 1930, to

GEORGE L. SCHWARTZ.

7 It is heieb y certified that error appears 'iWthe-printedspecification of rtheabove numbered patent requiring correction asfollows: Page 2, line 25, claim 1, for the word "fabrics" read fibers";and that the said Letters Patent should be read with this correctionthGI Bil'l that the same may conform to the record of the case in thePatent Office,

Signed and sealed this 24th'day of June, A. D. 1930.

r M. J. Moore, (Sea Actisg Commissioner of Patents.

